1. Field of the Invention
The present invention relates to a method of depositing a high permittivity dielectric film, and more particularly, a method of depositing a high permittivity dielectric film such as various oxide films or nitride films with very thin and uniform thickness on a silicon layer in a substrate.
2. Description of the Related Art
In making MOSFET devices on a silicon substrate, for example, the deposition of very thin films of dielectric materials with permittivity considerably higher than SiO2 will be very important for future semiconductor devices. The thin higher permitittivity dielectric film is used as a gate-dielectric layer in the MOSFET, for example. In detail, the high permittivity dielectric materials are expected for use in two different applications. The first application is to replace currently widely using SiO2, SiON and Si3N4 dielectric materials in CMOS transistor gate dielectrics. The second application is to fabricate capacitors with higher capacitance particularly for liquid crystal display panels.
At present there are two basic techniques in depositing high permittivity dielectric materials. The first method is chemical vapor deposition (CVD) and the second method is physical vapor deposition (PVD).
Even though there are many different techniques in depositing films by CVD method, basically two methods are widely used in industry. In the first technique, a chemical precursor, preferably a metal organic compound, is decomposed by a plasma or thermal energy and reacted with a suitable gas to form a desired higher permittivity dielectric material. This technique is usually referred to MO-CVD technique. In the second method, two chemical agents are introduced to a substrate alternately having a time-break in between each gas introduction. During the time-break, the first introduced gas is evacuated except molecules adsorbed on the substrate surface. When the second agent is introduced, it reacts with the surface adsorbed first gas molecules and forms a dielectric film. Then remaining excess gas is evacuated during the time break that goes until next gas introduction. This technique is referred to atomic layer deposition (ALD) technique.
There are two basic requirements in depositing the high permittivity dielectric films on the silicon substrate as the gate dielectric in the CMOS applications. The first requirement is that the film has to be very thin. For example, most of the future CMOS devices need films with a physical thickness less than 3 nm. The second requirement is that thickness of the films has to be extremely uniform, for example, less than 1% (1σ). Since these films are very thin, a slight non-uniform film significantly changes electrical properties, for example, capacitance and leakage current. With reference to these two basic requirements, demerits of above deposition techniques are discussed.
As one of conventional techniques there is JP-A-11-168096 disclosing a method of depositing high dielectric oxide films directly on silicon layers using a reactive sputtering method or CVD, for example. This method has been proposed for forming a high dielectric oxide film directly on the silicon layer without degrading the properties of the high dielectric oxide film, such as the high dielectric or insulation. In accordance with the above-mentioned conventional method, first, the high dielectric nitride film is formed on the silicon layer, and afterward the high dielectric nitride film is changed to become the high dielectric oxide film by oxidizing it.
When fabricating a very thin dielectric film used as a gate-dielectric layer in the MOSFET on the silicon substrate, a uniform dielectric film with a higher permitittivity is need to be deposited.